1. Field of the Invention
The present invention relates to an AC type plasma display panel, and more particularly to an electrode structure of a surface-discharge type plasma display panel.
2. Description of the Prior Art
A plasma display panel is classified into an AC type and a DC type and the AC type plasma display panel is further classified into a surface-discharge type and an opposed-discharge type.
A conventional surface-discharge type plasma display panel is shown in FIG. 12 and FIG. 13. As shown in FIG. 14, which is a cross section taken along a line Axe2x80x94A in FIG. 13, a front substrate 1 and a rear substrate 2 are arranged in an opposed relation so as to form a discharge space 10. The front and rear substrates 1 and 2 are formed of soda lime glass having thickness of 2 mm to 5 mm. A plurality of electrode pairs 3 each including transparent sustaining electrodes 3a and 3b of indium tin oxide are formed on the front substrate 1. To reduce electric resistance of the sustaining electrodes 3a and 3b, metal electrodes of silver or aluminum may be formed on the sustaining electrodes 3a and 3b, respectively. On the sustaining electrode pairs 3, a transparent dielectric layer 5 of low melting point glass is formed with thickness of 10 xcexcm to 40 xcexcm and then covered by an MgO protective film 8 having thickness of 0.5 xcexcm to 2 xcexcm.
A plurality of data electrodes 4 are formed on the rear substrate 2 and a white dielectric layer 6 is coated on the data electrodes 4. A phosphor layer 7 is then formed on the white dielectric layer 6.
The front substrate 1 and the rear substrate 2 are arranged in a mutually opposing relation in such a way that the electrode pairs 3 and the data electrodes 4 become orthogonal to each other, resulting in a plurality of cells 12. In the following description, a direction along which the data electrodes 4 extend will be referred to as xe2x80x9crow directionxe2x80x9d and a direction along which the electrode pairs 3 extend will be referred to as xe2x80x9cline directionxe2x80x9d.
The discharge space 10 of each cell 12 is filled with mixed rare gas containing Xe gas at a pressure of 20 kPa to 80 kPa. The cells 12 are partitioned by barrier ribs 11 extending in the row direction. In a case where each cell has a longitudinal length (row direction) of 1.05 mm and a lateral length (line direction) of 0.35 mm, for example, the sustaining electrodes 3a and 3b each 300 xcexcm to 450 xcexcm wide and 0.1 xcexcm to 2 xcexcm thick are arranged with a discharge gap 9 of 50 xcexcm to 300 xcexcm therebetween.
A sustaining voltage is applied between the sustaining electrodes 3a and 3b to generate sustaining discharge in the discharge space 10. Electrons generated by this discharge collide with Xe atoms, so that Xe atoms are excited or ionized. Excited Xe atoms emit ultraviolet ray having wavelengths 147 nm and 150 nm to 190 nm in vacuum ultraviolet region and the phosphor layer 7 irradiated with the ultraviolet ray emits visible light. The visible light is derived through the MgO protective film 8, the transparent dielectric layer 5, the sustaining electrodes 3a and 3b and the front substrate 1, directly or after reflected by the white dielectric layer 6.
The generated sustaining discharge is automatically terminated after charges are accumulated on a surface of the dielectric layer. For example, in a case where a positive pulse voltage is applied to the sustaining electrodes 3a and a negative pulse voltage is applied to the sustaining electrodes 3b, electrons generated by the discharge are moved to the sustaining electrodes 3a and positive ions such as Xe+ are moved to the sustaining electrodes 3b, so that the discharge terminates after the surface of the transparent dielectric layer on the sustaining electrodes 3a is charged negative and the surface of the transparent dielectric layer on the sustaining electrodes 3b is charged positive.
In order to reduce power consumption of the AC drive, surface-discharge type plasma display panel, it is necessary to improve the luminous efficiency thereof to thereby reduce power consumed by discharge. In general, there is a tendency that the lower the discharge current density results in the higher the luminous efficiency of the AC type plasma display panel. It is possible to improve the luminous efficiency of the plasma display panel by reducing the voltage to be applied to the sustaining electrodes to thereby reduce the discharge current since, in the latter case, the discharge current density is lowered. However, when the sustaining voltage is lowered, the discharge becomes unstable and, therefore, a stable display operation becomes impossible.
On the other hand, it is possible to reduce electrostatic capacitance between the surface of the transparent dielectric layer and the sustaining electrodes when an area of each sustaining electrode is reduced by reducing the width thereof. In a case where the same sustaining voltage is applied to the sustaining electrodes each having reduced width, it is possible to reduce discharge current since an amount of charge accumulated on the surface of the transparent dielectric layer is reduced. In such case, however, since the area of the sustaining electrodes is reduced, the discharge current density is unchanged. Therefore, the luminous efficiency is not changed substantially.
When the area of the sustaining electrodes is reduced, discharge does not spread over the cells, so that only a portion of the phosphor layer may emit light. As a result, luminance is lowered and it is impossible to obtain an acceptable image quality.
JP H08-22772A discloses a technique for improving luminous efficiency by using sustaining electrodes each including a main portion extending in a line direction and a protruded portion protruding from the main portion and having a narrowed portion. In this prior art, power consumption is reduced by reducing discharge current of each cell by the narrowed portion. In this prior art, however, there may be a case where luminance is reduced since discharge is concentrated in the vicinity of the narrowed portion and does not spread over the cells.
On the other hand, Japanese Patent No. 2734405 discloses a technique for reducing peak value of discharge current by providing an opening in each of sustaining electrodes arranged along a plurality of rows such that discharge current includes a plurality of peaks. However, in this prior art in which peaks of discharge current are separated, discharge current density is substantially equal to that of the conventional structure since the relatively large opening is formed in each sustaining electrode. Consequently, it is impossible to improve luminous efficiency.
Accordingly, an object of the present invention is to provide an AC type plasma display panel having improved luminous efficiency, improved luminance and small power consumption.
To achieve the above object, an AC type plasma display panel according to the present invention, which has electrodes formed on a substrate thereof and a dielectric layer covering the electrodes, is featured by that each of the electrodes is a mesh electrode having a plurality of openings and each opening has such size as included within a rectangular area having either side equal to or larger than 5 xcexcm and shorter than 30 xcexcm or has a strip shape having width equal to or larger than 5 xcexcm and shorter than 30 xcexcm.
In the present invention, a voltage signal for sustaining discharge is applied to the mesh electrodes and discharge is generated in a discharge space. Due to the use of the mesh sustaining electrodes each having a plurality of openings, an area of the sustaining electrode is reduced compared with the conventional structure and discharge current is reduced. Since, in the present invention, the size of the opening is as small as Debye length of discharge plasma, amounts of various physical factors featuring the discharge structure, such as electron density, ionization rate, excitation rate, etc., are not changed drastically. In such case, it is possible to uniformly reduce discharge current density spatially regardless of configuration of the opening.
Such effect can be obtained provided that the opening has the size included in a rectangular area having either side length in the order of Debye length of plasma or has a strip-shaped configuration having width in the order of Debye length. As a result, discharge current density is reduced and the luminous efficiency is improved. On the other hand, discharge spreads along the mesh electrode to cover the whole cell, resulting in sufficient luminance. Therefore, the AC type plasma display panel having improved luminous efficiency, improved luminance and low power consumption is realized.